Method and system for adjusting downlink outer loop power to control target sir

ABSTRACT

A wireless communication system and method for controlling transmission power to maintain a received signal-to-interference ratio (SIR) as close as possible to a target SIR. A received quality is maintained as close as possible to a target quality based on block error rate (BLER). When a target BLER is converted to an initial target SIR, an error may occur due to a channel condition mismatch, since the target SIR required for the target BLER varies with channel conditions. An outer loop power control process is used to set a target SIR for each coded composite transport channel (CCTrCH) based on the required target BLER. The process adjusts a SIR step size parameter to maximize the convergence speed of the process.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.10/771,576, filed Feb. 4, 2004, which is a continuation of U.S.application Ser. No. 10/659,673, filed Sep. 10, 2003, which issued asU.S. Pat. No. 7,133,689 on Nov. 7, 2006, which claims priority from U.S.Provisional Application No. 60/410,781, filed on Sep. 12, 2002, which isincorporated by reference as if fully set forth.

FIELD OF INVENTION

The present invention relates to the field of wireless communications.More specifically, the present invention relates to compensating forchanging channel conditions and by adjusting the step size of a targetsignal-to-interference ratio (SIR).

BACKGROUND

Spread spectrum time division duplex (TDD) systems carry multiplecommunications over the same spectrum. The multiple signals aredistinguished by their respective chip code sequences (codes). In oneconfiguration, TDD systems use repeating frames divided into a number oftime slots, such as fifteen time slots. In such systems, a communicationis sent in a selected time slot out of the plurality of time slots, andone frame is capable of carrying multiple communications distinguishedby both time slot and code. The combination of a single code in a singletime slot is referred to as a physical channel. Based on the bandwidthrequired to support a communication, one or multiple physical channelsare assigned to support that communication.

Most TDD systems adaptively control transmission power levels. In a TDDsystem, many communications may share the same time slot and spectrum.While a wireless transmit and receive unit (WTRU) is receiving adownlink transmission from a base station, all of the othercommunications using the same time slot and spectrum cause interferenceto the specific communication. Increasing the transmission power levelof one communication degrades the signal quality of all othercommunications within that time slot and spectrum. Reducing thetransmission power level too far results in undesirable signal to noiseratios (SNRs) and bit error rates (BERs) at the receivers. To maintainboth the signal quality of communications and low transmission powerlevels, transmission power control is used.

The purpose of power control is to use the minimum power required toadequately transmit a communication. One measure of power control in TDDfor example, may be to use the minimum power to allow each transportchannel (TrCH) to operate with a Block Error Rate (BLER) that does notexceed its required level. The standard approach to TDD downlink powercontrol is a combination of inner and outer loop control. In thisstandard approach, a base station sends a transmission to a particularWTRU. Upon receipt, the WTRU measures the SIR in all time slots andcompares this measured value to a target SIR. This target SIR isgenerated from the BLER signaled from the base station. As a result of acomparison between the measured SIR value and the target SIR, the WTRUtransmits a physical layer transmit power control (TPC) command to thebase station. The standard approach provides for one TPC command percoded composite transport channel (CCTrCH). The CCTrCH is a physicalchannel which comprises the combined units of data for transmission overthe radio interface to and from the WTRU or base station. This TPCcommand instructs the base station to adjust the transmission powerlevel of the downlink communication. The base station, which is set atan initial transmission power level, receives the TPC command andadjusts the transmit power level in all time slots associated with theCCTrCH in unison.

An inner loop power control process controls transmit power to maintainthe received SIR as close as possible to a target SIR by monitoring theSIR measurements of the data. An outer loop power control processcontrols the target SIR to maintain the received quality BLER as closeas possible to a target quality BLER based on a cyclic redundancy code(CRC) check of the data. The output from the outer loop power control isa new target SIR per CCTrCH used for the inner loop power control.

There are four main error sources in transmission power control: 1)systematic error; 2) random measurement error; 3) CCTrCH processingerror; and 4) channel error. The systematic error and the randommeasurement error are corrected reasonably by the inner loop powercontrol monitoring the SIR measurements. The CCTrCH processing error iscorrected by either the outer loop power control or the inner loop powercontrol by using relative SIR measurements among the codes. The channelerror is related to unknown time varying channel conditions.

In power control systems, the outer loop power control process sets atarget SIR for each CCTrCH based on the required target BLER, assuming amost plausible channel condition. Therefore, the mismatch between thetarget BLER and the mapped target SIR varies depending on the actualchannel condition, and it is especially large at very low BLER. Sincethe outer loop power control depends on the CRC check, it often takes along time to converge to the required target SIR for the low BLER.

Accordingly, there is a need for outer loop power control whichdetermines the actual channel conditions so that a proper value for thetarget SIR is used.

SUMMARY

Outer loop power control is performed in a series of iterations. Afterinitial parameters are set, a transient state optimization of SIRs basedon errors is performed in incremental steps. A determination is thenmade of a steady state.

In one configuration, an outer loop power process is used to controltransmit power by monitoring SIRs and adjusting the power process tocontrol a target SIR so as to maintain a received signal quality asclose as possible to a target quality. Mismatch errors are evaluated byBLER as a measurement of received quality, and an output from the outerloop power may be used to obtain a new target SIR, thereby quicklycompensating for a mismatch in SIR when channel conditions change. Theinvention finds particular utility for use in a digital wirelesscommunications network.

BRIEF DESCRIPTION OF THE DRAWING(S)

The objectives of the present invention will become apparent uponconsideration of the accompanying detailed description and figures, inwhich:

FIG. 1 shows typical downlink simulation results of WCDMA TDD forvarious channel conditions specified in 3GPP using a zero-forcingmulti-user detector;

FIG. 2 is a graph of a target SIR versus a number of TrCH blocks used bya jump algorithm;

FIG. 3 illustrates the different states of an exemplary target SIRadjustment process used in accordance with the present invention; and

FIGS. 4A, 4B and 4C, taken together, is a flow chart of the SIRadjustment process of FIG. 3.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

Presently preferred embodiments are described below with reference tothe drawing figures wherein like numerals represent like elementsthroughout.

Although the preferred embodiments are described in conjunction with athird generation partnership program (3GPP) wideband code divisionmultiple access (W-CDMA) system utilizing the time division duplex mode,it is to be noted that the invention in its broad form is alsoapplicable to other systems of transmission, without limitation. Forexample, the embodiments are applicable to any closed loop power controlapplication and may be applied to frequency division duplex (FDD), timedivision synchronous code-division multiple access (TDS CDMA), CDMA2000,and IEEE standard 802.11.

Hereafter, a wireless transmit/receive unit (WTRU) includes but is notlimited to a user equipment, mobile station, fixed or mobile subscriberunit, pager, or any other type of device capable of operating in awireless environment. When referred to hereafter, a base stationincludes but is not limited to a base station, Node-B, site controller,access point or other interfacing device in a wireless environment.

Transmit power control processes may comprise an inner loop powercontrol, an outer loop power control, or a combination of inner loop andouter loop power control. In accordance with the present invention, bothinner loop and outer loop power control processes are employed. Theinner loop power control process controls transmit power to maintain thereceived SIR as close as possible to a target SIR by monitoring the SIRmeasurements of the data. The outer loop power control process controlsthe target SIR to maintain the received quality as close as possible toa target quality. A typical measurement of received quality is BLERbased on a CRC check of the data. The output from the outer loop powercontrol is a new target SIR used for the inner loop power control.

Since the channel condition is not known, the outer loop power controlprocess converts the required target BLER to a target SIR based upon a“most plausible” channel condition. For example, FIG. 1 shows typicaldownlink simulation results of WCDMA TDD for various channel conditionsspecified in 3GPP using a zero-forcing multi-user detector. Results areshown for various propagation conditions. Additive white Gaussian noise(AWGN) is the static channel, while Case 1 through 3 are fading channelswith different multipath profiles. At a required BLER of 0.01 for a Case1 fading channel, a predetermined transmission power can be determinedfrom the target SIR of approximately 4.5 dB. Note that this is more than5 dB over the target SIR for the case 2 fading channel and more than 12dB over the target SIR for AWGN, illustrating the large span of SIRvalues depending on the assumed propagation condition. Therefore atarget SIR could be selected based on Case 1 or an average of allchannel conditions (AWGN, Case 1, 2, 3).

Based on the above example, the mismatch between the required BLER andthe mapped target SIR varies depending on the actual channel conditionand it is large especially at very low BLERs. Since the outer loop powercontrol depends on the CRC check, it will take a long time to convergeto the required target SIR for the low BLER. Hence the fast convergentprocess of the present invention attempts to quickly compensate for themismatch between the assumed and actual channel conditions andaccelerate the convergence speed when excessive target SIR occurs due toa favorable change in the channel conditions by increasing step size ofthe jump algorithm temporarily.

FIG. 2 is a graphical illustration of the results of employing a jumpalgorithm in accordance with the present invention. The DL outer looppower control process basically utilizes the jump algorithm that adjustsa target SIR based on the result of CRC check of the data at varyingrates of TrCH blocks per transmission time interval (TTI).

As will be explained in greater detail hereinafter, the DL outer looppower control process comprises three states: the inner loop settlingstate, the transient state, and the steady state.

In the inner loop settling state, the inner loop transmission powercontrol (TPC) process corrects the initial system systematic error andthe random measurement error without changing the initial target SIR.

In the transient state, the outer loop power control process attempts tocorrect the initial target SIR error caused by the channel conditionmismatch. Initially, the jump algorithm in the transient state uses alarge step size to decrease the target SIR rapidly, (i.e., it forces aCRC error to occur). The initial large step size is calculated basedupon the target BLER and the number of transport blocks per TTI (N_(b))for the reference TrCH as follows:SIR_step_size=2*[log₁₀(1/BLER)]/N _(b) dB.  Equation (1)

Once a CRC error occurs, the step size is reduced to one half and thenapplied to the jump algorithm. The same procedure iterates until the newstep size converges to the step size of the steady state, which iscalculated as follows:SIR_step_size=0.25[log₁₀(1/BLER)]/N _(b) dB.  Equation (2)

In the steady state, the target SIR is adjusted up or down with thesteady state step size based on each CRC check. If no CRC error occurswithin a long observation period (5/BLER consecutive transport blocks),the SIR_step_down is temporarily doubled.

Alternatively, the steady state is changed back to the beginning of thetransient state such that the step size is set to the initial large stepsize and is gradually reduced to one half whenever a CRC error occurs.This improves the convergence time when a sudden improvement in channelconditions occurs, giving rise to an excessive measured SIR compared tothe desired target SIR.

FIG. 3 shows the three different states of an exemplary SIR adjustmentprocess. In this example, several transport blocks are received withoutCRC error after the transient state is entered, resulting in multipledecreases (see points A1, A2, A3, A4, A5, A6) of Td in the target SIR.At point A6, Td represents the initial value of SIR_step_down. A CRCerror then occurs, and the target SIR is increased by Tu/2 to point A7.At point A7, Tu represents the initial value of SIR_step_up. The CRCerror also causes an adjustment in the step down size whereby subsequenttransport blocks received without a CRC error result in a decrease intarget SIR by Td/2 (see points A8, A9, A10, A11, A12).

When the next CRC errors occurs, the step up size is reduced to Tu/4 atpoint A13, target SIR is increased by that amount, and the step downsize is adjusted to Td/4 (see points A14, A15, A16, A17, A18). Thisprocess continues until the adjusted step up size equals the steadystate step up, which in this example is equal to Tu/8 at point A19. Atpoint A19, steady state is entered, and the step up and step down sizesare fixed at Su and Sd, respectively, in which Su is steady state valueof SIR_step_up (see point A28) and Sd is the steady state value ofSIR_step_down (see points A20, A21, A22, A23, A24, A25). When no CRCerror occurs for 5/BLER consecutive transport blocks, the step down sizeis temporarily increased to 2*Sd (see points A26, A27). It remains atthat value until a CRC error occurs, when it is then returned to Sd (seepoints A29, A30). The steady state continues for the life of the CCTrCH.The process may return to the transient state to reduce convergencetime. Since the transient state uses the larger step size, the responsetime is faster, i.e., it reduces convergence time.

This example is based on the variable that the first transport blockafter settling state is received without error, and the target SIR isdecrease by Td. It is possible that the initial CRC result can indicatean error, which would result in an initial increase in target SIR byTu/2, and setting of the step down size to Td/2. It is also possible(but not shown in this example) that the first CRC result after a stepup indicates an error. In this case, target SIR is increased again, butby half the previous increase (i.e., if a CRC error occurs and targetSIR is increased by Tu/4, and the next CRC result also indicates anerror, the target SIR is increased by Tu/8, and the step down size isset to Td/8).

In this example only one transport block is received in each TTI. Ifmore than one transport block is received, each good CRC will result ina step down, and each CRC error will result in a step up, but the stepsize will only be adjusted once per TTI (at the beginning) and only ifat least one CRC error is present in the TTI: the outer loop processfirst determines whether any CRC errors occur in this new TTI, adjuststhe up and down step sizes appropriately, then applies the stepadjustments based on the individual CRC results.

For example, consider a TTI with four transport blocks, three of whichindicate a CRC error. If the step up size is Tu/2 and the step down sizeis Td/2 prior to this TTI, the outer loop process will first adjust thestep sizes to Tu/4 and Td/4, and then update the target SIRappropriately. The net result is thattargetSIRnew=targetSIRold−(Td/8)+3*(Tu/8).

In both the transient and steady states, if the reference TrCH changes(i.e., for variable bit rate (VBR) services), and the BLER of that newreference is different from the old, the SIR step sizes are recalculatedbased on the new target BLER. In steady state, the observation period isalso updated, and the current count of blocks without error is reset to0. In transient state, in addition to recalculating the step sizes, anadditional adjustment is be made to account for the “convergence” thatmay already have occurred in this state. For example, if the currentstep down size before reference TrCH reselection is Td_(old)/4, then thestep down size immediately after TrCH reselection is be set toTd_(new)/4 and the step up size is be set to Tu_(new)/4. Thus, thecalculated values are divided by 2^(n), where n is the number of TTIssince the start of transient state that contained at least one CRCerror.

FIGS. 4A-4C, taken together, is a flow chart of an exemplary downlinkouter loop power control process 400 including a settling state 405 (seeFIG. 4A), transient state 410 (see FIG. 4B) and a steady state 415 (seeFIG. 4C). After starting (step 420), the process 400 enters the settlingstate 405 in which initialization parameters are set (step 425). In theexample, the parameters are set at:

-   -   inner loop settling time=100 ms;    -   steady state step size=(0.25*log₁₀(1/BLER)/N_(b));    -   transient state step size=(2*log₁₀(1/BLER)/N_(b)); and    -   TTI count=0.

The inner loop settling time is based on the inner loop power controlsettling time and is used to compensate for systematic errors. N_(b) isdefined as the number of transport blocks per TTI. N_(e) is defined asthe number of CRC errors per TTI for the reference TrCH.

In step 430, a decision is then made as to whether the resulting productof multiplying the TTI count by the TTI length is greater than the innerloop settling time. Each TTI consists of N_(b) blocks, depending on thedata rate. Each block has a CRC. N_(e) is the number of CRC errorswithin a TTI, i.e., N_(e) CRC errors out of N_(b) blocks per TTI. If theresulting product is not greater than the inner loop settling time, theTTI count is incremented (step 435) and step 430 is repeated. If theresulting product is greater than the inner loop settling time, theprocess goes to the transient state 410, in which computer parametersfor a jump algorithm are set (step 440). The parameters may be:

-   -   step size=transient state step size;    -   step down=BLER*(step size); and    -   step up=step size−step down.

In step 445, a determination is made as to whether the step size isgreater than the steady state step size. If the transient state stepsize is determined in step 445 to be less than or equal to the steadystate step size, then the process 400 goes to the steady state 415. Ifthe transient state step size is determined in step 445 to be greaterthan the steady state step size, then a determination is made in step450 as to whether the number of CRC errors in the respective TTI forN_(e) is greater than zero. If the number of errors is determined not tobe greater than zero in step 450, then target SIR is decreased (step455). In the decrease of the target SIR, the target SIR is determined tobe equal to the (target SIR)−(step down*N_(b)).

If the target SIR is less than a minimum DL SIR, the target SIR isdeemed to be the minimum DL SIR. If the number of CRC errors isdetermined in step 450 to be greater than zero, the parameters for thejump algorithm are adjusted (step 460). In adjusting the parameters, thestep size is set at half the previous step size. If the step size isless than the steady state step size, the step size is set at the steadystate step size, the step down is set at (BLER)*(step size), and thestep up is set at (step size)−(step down). When the target SIR isincreased in step 465, the target SIR is set at (target SIR)+(stepup)*(N_(e)))−(step down)*(N_(b)−N_(e)). If the target SIR is greaterthan the maximum DL SIR, the target SIR is deemed to be the maximum DLSIR. The process is looped so that after step 455 or 465, the processreturns to step 445.

The steady state 415 is initiated after the step size is no longergreater than the steady state step size as determined in step 445. Atthat time, initial steady state parameters are set in step 470, inwhich:

-   -   step size=steady state step size;    -   step up=step size−BLER*(step size); and    -   lapse count since the last CRC error=0.

A determination is then made (step 475) as to whether the lapse countsince the last CRC error is greater than (5/BLER). If not, then the stepdown is established at (BLER)*(step size) (step 480). If the lapse countis greater than 5/BLER, the step down is set at 2*(BLER)*(step size)(step 482). In either case, a determination (step 490) is made as towhether the number of CRC errors in this TTI (N_(e)) is greater thanzero. If the number of CRC errors is determined not to be greater thanzero in step 490, then target SIR is decreased (step 495) where thetarget SIR is determined to be equal to the (target SIR)−(stepdown*N_(b)) and the lapse count since the last CRC error is incrementedby N_(b). If the target SIR is less than a minimum DL SIR, the targetSIR is deemed to be the minimum DL SIR.

If the number of CRC errors is determined to be greater than zero instep 490, the target SIR is increased (step 492) where the target SIR isset at (target SIR)+(step up)*(N_(e)))−(step down)*(N_(b)−N_(e)). Thelapse count since the last CRC error is reset to zero. If the target SIRis greater than the maximum DL SIR, the target SIR is deemed to be themaximum DL SIR. The process is looped so that after step 492 or 495, theprocess returns to step 475.

If there are multiple blocks per TTI for the reference TrCH within aCCTrCH(=N_(b)), the target SIR will be adjusted as follows:target SIR=target SIR+step_up*N _(e)−step_down*(N _(b) −N _(e))where N_(e) is defined as the number of CRC errors per TTI for thereference TrCH.

While the present invention has been described in terms of the preferredembodiment, other variations which are within the scope of the inventionas outlined in the claims below will be apparent to those skilled in theart.

1. A method of transmission power control for a wireless transmitreceive unit (WTRU) that transmits data signals in a forward channelwhere the WTRU is configured to make forward channel power adjustmentsas a function of target metrics computed based on the data signals asreceived over the forward channel, the method comprising: receiving datasignals from the WTRU on the forward channel; and computing targetmetrics for the WTRU's forward channel power adjustments based on thedetection of predetermined error conditions in the signals received onthe forward channel, wherein an initial target metric value is set and,after a preliminary period at the initial value, the target metric ischanged by a step up or a step down amount at time intervals of apredetermined length, and the step up and step down amounts are set to afirst relatively high transient state level and are reduced by aselected amount if a predetermined error condition has been detected inan immediately preceding time interval until the step up and step downamounts are reduced to a second relatively low steady state level. 2.The method of claim 1 wherein the step of computing target metricsfurther includes increasing the step up and step down amounts by aselected amount if a predetermined error condition has not been detectedin a predetermined number of time intervals while they are set at thesecond relatively low steady state level.
 3. The method of claim 1wherein the target metric is increased by the step up amount if apredetermined error condition has been detected in an immediatelypreceding time interval or is decreased by the step down amount if thepredetermined error condition has not been detected in the immediatelypreceding time interval.
 4. The method of claim 1 wherein the targetmetrics are target signal to interference ratios (SIRs) and cyclicredundancy checks are conducted to detect the predetermined errorcondition.
 5. The method of claim 1 wherein step up amounts aresignificantly greater than respective step down amounts, the first levelof step up and step down amounts are a factor of 2^(n) greater then thesecond level of step up and step down amounts, where n is a positiveinteger, and the step up and step down amounts are reduced by a factorof ½ if a predetermined error condition has been detected in animmediately preceding time interval until they are reduced to the secondlevel.
 6. The method of claim 5 wherein the step of computing targetmetrics further includes increasing the step up and step down amounts bya factor of 2 if a predetermined error condition has not been detectedin a predetermined number of time intervals while they are set at thesecond relatively low steady state level.
 7. The method of claim 5wherein the step of computing target metrics further includes increasingthe step up and step down amounts to the first level if a predeterminederror condition has not been detected in a predetermined number of timeintervals while they are set at the second relatively low steady statelevel.
 8. The method of claim 1 wherein the WTRU is a network unit thattransmits user signals on a downlink channel and the step of computingof target metrics is performed by a WTRU that receives the downlinkchannel.
 9. The method of claim 1 in which closed loop transmissionpower control for the transmitting WTRU is implemented, the methodfurther comprising: the receiving WTRU producing power step commands asa function of the target SIRs and transmitting the power step commandson a reverse channel; and the transmitting WTRU receiving the power stepcommands on the reverse channel and computing power adjustments forforward channel transmissions based on the received power step commands.10. The method of claim 9 wherein the method is implemented in a thirdgeneration partnership program (3GPP) wideband code division multipleaccess (W-CDMA) system where the transmitting WTRU is a network unitthat transmits user signals on a downlink channel and the step ofcomputing target metrics is performed by the receiving WTRU thatreceives the downlink channel and produces power step commands that aretransmitted to the network unit on an uplink channel.
 11. A receivingwireless transmit/receive unit (WTRU) for implementing transmissionpower control for a transmitting WTRU that transmits data signals in aforward channel, the transmitting WTRU being configured to make forwardchannel transmission power adjustments as a function of target metricscomputed by the receiving WTRU, the receiving WTRU comprising: areceiver for receiving data signals from the transmitting WTRU on theforward channel; and a processor for computing target metrics forimplementing forward channel transmission power adjustments in thetransmitting WTRU based on the detection of predetermined errorconditions in the data signals received on the forward channel, whereinthe processor is configured to compute target metrics such that aninitial target metric value is set and, after a preliminary period atthe initial value, the target metric is changed by a step up or a stepdown amount at time intervals of a predetermined length, and the step upand step down amounts are set to a first relatively high transient statelevel and are reduced by a selected amount if a predetermined errorcondition has been detected in an immediately preceding time intervaluntil the step up and step down amounts are reduced to a secondrelatively low steady state level.
 12. The receiving WTRU of claim 11wherein the processor is further configured to compute target metricssuch that the step up and step down amounts are increased by a selectedamount if a predetermined error condition has not been detected in apredetermined number of time intervals while they are set at the secondrelatively low steady state level.
 13. The receiving WTRU of claim 11wherein the target metric is increased by the step up amount if apredetermined error condition has been detected in an immediatelypreceding time interval or the target metric is decreased by the stepdown amount if the predetermined error condition has not been detectedin the immediately preceding time interval.
 14. The receiving WTRU ofclaim 11 in which the target metrics are target signal to interferenceratios (SIRs) and the receiving WTRU is configured to conduct cyclicredundancy checks to detect the predetermined error condition.
 15. Thereceiving WTRU of claim 11 wherein the processor is configured tocompute target metrics such that step up amounts are significantlygreater than respective step down amounts of a given level, the firstlevel of step up and step down amounts are a factor of 2^(n) greaterthen the second level of step up and step down amounts, where n is apositive integer, and the step up and step down amounts are reduced by afactor of ½ if a predetermined error condition has been detected in animmediately preceding time interval until they are reduced to the secondlevel.
 16. The receiving WTRU of claim 15 wherein the processor isfurther configured to compute target metrics such that the step up andstep down amounts are increased by a factor of 2 if a predeterminederror condition has not been detected in a predetermined number of timeintervals while they are set at the second relatively low steady statelevel.
 17. The receiving WTRU of claim 15 wherein the processor isfurther configured to compute target metrics such that the step up andstep down amounts are increased to the first level if a predeterminederror condition has not been detected in a predetermined number of timeintervals while they are set at the second relatively low steady statelevel.
 18. The receiving WTRU of claim 11 where the transmitting WTRU isa network unit that transmits user signals on a downlink channel whereinthe receiving WTRU is configured to compute target metrics based on thedetection of predetermined error conditions in the data signals receivedon the downlink channel.
 19. The receiving WTRU of claim 12 in whichclosed loop transmission power control for the transmitting WTRU isimplemented, wherein the receiving WTRU processor is further configuredto produce power step commands as a function of the computed targetSIRs, and the receiving WTRU is further configured to transmit the powerstep commands on a reverse channel to the transmitting WTRU.
 20. Thereceiving WTRU of claim 19 wherein the receiving WTRU is used in a thirdgeneration partnership program (3GPP) wideband code division multipleaccess (W-CDMA) system where the transmitting WTRU is a network unitthat transmits user signals on a downlink channel wherein the receivingWTRU is configured to compute target metrics based on the detection ofpredetermined error conditions in the data signals received on thedownlink channel.